Solvent extraction of wax-bearing oils



1936- s. H. mess ET AL 2,063,369

SOLVENT EXTRACTION OF WAX BEARING OILS Filed Feb. 23, 1932.

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Patented Dec. 8, 1936 UNITED STATES PATENT orrlcs Sterling H. Diggs andJames M. Page, Jr., Casper, Wyo., assignors to Standard Oil Company,Chicago, Ill., a corporation of Indiana Application February 23, 1932,Serial No. 594,612

9 Claims. (01. 19c 17) This invention relates to a system for extractingundesirable components from an oil-wax mixture and it pertains moreparticularly to the separation of naphthenic from paraflinicconstituents in a mixed base petroleum lubricating oil stock.

A recent innovation in the petroleum art has been the separation ofparaflinic from naphthenic components by means of certain selectivesolvents. One solvent which has proven to be of outstanding superiorityis dichlorethyl ether- ClCH2CH2OCH2CH2Clwhich has a boiling point ofabout 352 F. (175 C.), a freezing point of about -61 F. (-51.7 C.) and aspecific gravity at 20 C. of about 1.22. In carrying out the extractionit is the usual practice to mix the oil and solvent at a temperatureabove the melting point of the paraffin which it may contain. When sucha mixture of wax-bearing oil and dichlorethyl ether is cooled, a largeamount of wax is thrown out of solution in the form of a buttery masswhich is diflicult to handle and which interferes with the separationof'parafiln oils from the dichlorethyl ether solution. The object of ourinvention is to provide a system and a process which will avoid thisdimculty and which will thereby facilitate the rapid separation ofparaffin oil from solvent solutions. In our preferred example we willdescribe the invention as applied to a dichlorethyl ether extraction,but it should be understood that any suitable solvent may be employed,providing its miscibility temperature is within the desired range.

A further object is to reduce the sulfur content, increase the viscosityindex, and decrease the sludge-forming tendency of lubricating oil.

A further object is to provide an improved means for separating the waxfrom lubricating oil. Other objects will be apparent as the detaileddescription of our invention proceeds.

In practicing our invention we remove the bulk of the wax in the liquidstate so that it cannot separate out in the later steps of theextraction process. We have discovered that when solvents of the classdescribed, such as dichlorethyl ether, are mixed with a wax-bearing oilat a temperatureabove the melting point of the wax and sufficiently highto give a homogeneous solution of oil and solvent, the first oil toseparate on cooling will contain the largest proportion of the wax. Byavoiding cooling below the solidification point of the wax bearing oilit may be readily separated while it is still in the liquid state. Thismay be accomplished by decantation or by the use of a continuous liquidseparator. Accordingly, in

practicing our invention we use a solvent which is immiscible with theoil-wax mixture at a temperature above the melting point of wax, and weprefer to remove the wax from the mixture by removing the first and, ifdesired, successive increments of the liquid which are thrown out ofsolution on cooling. When practically all of the wax has been removed,the extraction may be carried out at relatively low temperatures, andthe two layers may be readily and rapidly separated without seriousinteri'erence from solidified wax.

The invention will be more clearly understood from the followingdetailed description of a preferred embodiment, reference being made tothe accompanying drawing which forms a part of this specification andwhich diagrammatically illustrates the same.

The invention will be described as applied to a waxy lubricating oilstock having a Saybolt viscosity of 83 at'210 F., a cold test of 122 F.,and a wax content of about 20%. This oil is commonly known as motor basestock and it is preferably a heavy distillate, although it may be aresidual oil. When this oil is extracted at 40 F. with one or twovolumes of dichlorethyl ether, a large amount of butter-like solid isformed. As a consequence, some of the solution is occluded in the solidand the efliciency of the extraction is seriously impaired.

In accordance with our invention, the waxbearing oil from storage tank Iis introduced by.

pipe I l to mixer l2, where it is thoroughly mixed with one and one-halfto two or more volumes of dichlorethyl ether from storage tank l3 andpipe I. The mixer may be of any suitable type, and is preferably theso-called orifice mixer which consists of a series of perforated bafliesin a cylindrical casing. Since the oil has a cold test of 122 F. it mustbe passed through the mixer in heated condition and we prefer tomaintain-both the oil stock and the dichlorethyl ether at a temperatureof about 145-170" F. If a temperature of 165 is obtained, thisparticular stock will be completely miscible with the solvent so thatlittle mixing will be necessary. 'Altematively, we may save aconsiderable amount of heat by using the mixer and employing a lowertemperature.

The mixture at about 145-170" F. is then introduced by pipe I 5 intosettling or separator tank I6. 11' the mixture is already at atemperature of about 145 F. there is no necessity for heating or coolingthe mixture in the settling tank. Therefore, this tank may act as acontinuous liquid separator. On the other hand, if the incoming mixtureis at a temperature of about 165-470 F. we must cool the liquid by meansof suitable coils ii. A slow, even stirring is desirable in the coolingtank; this may be accomplished by the use of centrifugal motion ashereinafter described, or it may be effected by suitable paddles orstirring means. Dichlorethyl ether is completely miscible with thisstock at 165 1"., and when the temperature is reduced to 145 1". about50% of the stock separates from the solution. The material separating atthis temperature is largely liquid wax and it constitutes about 75% ofthe wax in the stock. As 145 1'. is well above the melting point of theoilwax mixture, it remains in the liquid phase, and it is a simplematter to remove it through pipe I! while the dichlorethyl ethersolution is being withdrawn from the base of the separator through pipel9.

We next cool the solution in cooler 20 to a temperature of about l25-l30F. and introduce it through pipe 2i into the second wax separationchamber 22. This chamber is also provided with coils 23 for supplyingheating or cooling fluids, if desired. In separating chamber 22 another25% of the wax is separated from the solution together with sufllcientoil which maintains it in the liquid state at a temperature even belowthe melting point of the wax.

If the solution were initially cooledto 130 F. the separated layer of anoil would have a strong tendency to solidify because of the largeproportion of wax in the mixture and the higher average melting pointthereof. Separation would be made diflicult and the efllciency ofextraction would be lowered. .(In accordance with our invention,however, we use a solvent which is immiscible with the wax at atemperature above its melting point and we remove the wax in incrementsso that nearly all of it may be removed as a liquid.)

The wax and oil are discharged from the top of the second wax separatorchamber through pipe 24 and the solvent is withdrawn from the base ofthe chamber through pipe 25. The solvent is then cooled in cooler 28 toa temperature of about 30-40 F. and introduced by pipe 21 into theseparation chamber 28. At this low temperature practically all of theparafiinic components of the oil are thrown out of solution andpractically all of the undesirable naphthenic constituents remaindissolved in the dichiorethyl ether. The temperature may be regulated bypassing heating or cooling fluids through coils 29, the paraillniccomponents are withdrawn from the top of the extraction chamber throughpipe 30 and the solvent with its naphthenic content is withdrawn throughpipe 3|.

If desired, the liquid wax from pipe It may be withdrawn through pipe 32to a/suitable system for removing the oil from the wax. Likewise, themixture from pipe 24 may be discharged through pipe 33 and the parafilnoil from pipe 30 may be discharged through pipe 34. On the other hand,we may combine these three fractions by header 35 and introduce them allinto still 86 for driving out traces of solvent, this solvent beingconducted through pipe 31 and condenser 38 to storage chamber II. Oilfrom the base of the still is withdrawn through pipe 40 to a suitabledewaxing systems The solvent from extraction chamber 28 is introduced bypipe 3| into still H, the naphthenic components being discharged throughpipe 42 and the solvent being expelled through pipe 43 and condenser 44back to the storage tank It.

The lubricating oil obtained from the dewaxed parafiln components ischaracterized by an extremely high viscosity index. In other words, thechange in viscosity with temperature is approximately the same as thechange of viscosity of natural paramn type oils which are rated ashaving a viscosity index of 100. The oils are characterized by a lowsulfur content and they are also found to be remarkably resistant tosludge formation.

While we have described in detail a preferred embodiment of ourinvention it should be understood that we do not limit ourselves to anyof the details herein set forth. The settling chambers or continuousliquid separators are shown diagrammatically, and it is understood thatany conventional equipment may be used for this purpose. Centrifugalseparators are particularly useful and we contemplate the use ofcentrifugal action obtained by introducing the mixtures tangentially atthe center of a vertical cylindrical tank, withdrawing the heavydichlorethyl ether solution at the periphery of the base and withdrawingthe lighter oil in the center of the top. The rotation of the liquidswill accelerate the separation thereof.

Dichlorethyl ether is illustrative of a large class of selectivesolvents which we may use for the separation of wax-containingparafilnic oils from the naphthenic 011 components by our process. Otherexamples are phenol, ethylene chlorohydrin, glycerol monohydrin,furfural, aniline, 2-4 dinitrochlorobenzene, butyl carbinol,phenylmethanol, etc. Acetone, nitrobenzene, chloroacetone, glycolacetate (cellosolve), 2 methyl propanol, and a large number of othersolvents may be used on stocks which have a sufiiciently low pour point.The essential feature of the invention is that the wax (or oil-waxmixture) should be in liquid form at a temperature at which it isimmiscible with the solvent.

The temperatures given in the preferred example are illustrative onlyand it will vary, of course, with other oil stocks and other selectivesolvents. For Mid-Continent lubricating oils the temperature for thefirst separation will probably be about to 1".

The layer insoluble at the high temperature may contain somedichlorethyl ether, which will, of course, be separated out at lowertemperatures.

We have found that the oil from the layer insoluble at high temperaturesis often materially better than the oil from the later separations. Forinstance, oil from the -145 insoluble lay.- er has a viscosity index of86.2, while oil from the top layer at 40 F. has a viscosity index ofonly 75.3 in tests made on oil from a Casper crude.

We claim:-

l. The method of removing wax from oil which comprises addingdichlorethyl ether to an onwax mixture, and separating the solublenaphthenic portions from the insoluble waxy portions of the mixture at atemperature above the melting point of the oil-wax mixture.

2. The method of obtaining maximum yields of high viscosity index oilsfrom a mixture of paraillnic and naphthenic components in a waxbearinglubricating oil stock, which comprises intimately mixing said stock witha solvent of the class which consists of dichlorethyl ether, phenol,furfural, aniline and nitrobenzene at a temperature above the pour pointof the waxbearing stock, efl'ecting phase separation at a hightemperature at which wax is separable as a liquid, removing the highviscosity index oil and wax which is insoluble in the solvent from saidsolvent solution at said high temperature, subsequently cooling saidsolvent solution and efiecting a phase separation of the remaininglubricating oil stock and solvent at a substantially lower temperaturewhereby substantially all of the desirable paraflinic components areseparated from the solvent, removing the low temperature solventsolution from the insoluble oil layer, and separately recovering thesolvent from the solution and from said insoluble oil fractions.

3. The method of removing wax from an oilwax mixture which comprisesdiluting said mixture with a preferential oil solvent, intimatelycontacting said solvent with said mixture at a temperature above themelting point of the mixture, separating the undissolved waxy part ofthe mixture from the solution at a temperature above the melting pointof the mixture, cooling the mixture to cause a further separation of theparaflinic liquids from the solution, and separating said liquidstherefrom.

4. The method of refining a lubricating oilwax mixture which comprisesadding dichlorethyl ether to said mixture, intimately mixing the same ata temperature at which all of the wax is in liquid state, separating thesolution from the undissolved liquids at a temperature above the pourpoint of said undissolved liquids, cooling the solution to separateparaflinic components from the naphthenic components of the oil, andseparating the paraffinic components from the solution.

5. The combination of claim 4, which includes the further step ofseparating liquid wax and oil from the solution at an intermediatetemperature.

6. The method of refining a petroleum oil which contains wax, parafllnicand naphthenic components, which comprises admixing said oil withdichlorethyl ether at a temperature near that at which the mixture iscompletely miscible, intimately mixing said oil and dichlorethyl etherat said temperature, cooling said mixture to etfect the separation of anoil phase containing liquid wax and paraflinic components and an etherphase containing naphthenic components, removing the oil phase from thenaphthenicdichlorethyl ether phase, cooling the latter phase to a lowertemperature to effect further phase separation, and removing the furtherseparated parafllnic oil from the solution of naphthenic components inthe separated dichlorethyl ether.

7. The method of fractionating a wax-bearing petroleum oil intofractions grading from paraffinic to naphthenic, which comprises mixingsaid oil with dichlorethyl ether at a temperature near that at which theoil is miscible with the dichlorethyl ether and above the pour point ofthe waxing oil, cooling the mixture in stages, separating wax as aliquid after the first cooling stage and separating paraflinic fromnaphthenic fractions after the subsequent cooling stages.

8. The method of refining a mixed base waxbearing mineral lubricatingoil, which comprises admixing it with dichlorethyl ether at atemperature of about 145-170" F., separating the undissolved liquid fromthe solution at a temperature of about 145 F. whereby a large proportionof wax is removed from the solution in the liquid state, cooling thesolution to about 130 F. and removing a further amount of waxy oil fromthe solution at said temperature, cooling the solution to about 30-40F., and separating the solution from the undissolved oil at saidtemperature, the solution containing the naphthenic components and theundissolved oil containing the paraillnic components of the oil.

9. The method of making a lubricating oil from a petroleum oilcontaining paraflinic components, naphthenic components and wax, whichcomprises mixing said oil with at least an equal volume of dichlorethylether, heating the mixture to a temperature of at least 125 F., coolingthe mixture to a temperature of about 30 F. to cause separation ofparafllnic from naphthenic components, removing the parafllniccomponents from the naphthenic components, and removing wax .from theparafllnic components.

STERLING H. DIGGS. JAMES M. PAGE, JR.

